linux-kernel - Re: [PATCH] pps: parport: use timespec64 instead of timespec

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Message-ID: <4da3970c-fb8a-89ac-f7f0-98d9e7df147b@enneenne.com>
Date:   Tue, 28 Nov 2017 10:16:45 +0100
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pps: parport: use timespec64 instead of timespec

On 27/11/17 12:43, Arnd Bergmann wrote:
> getnstimeofday() is deprecated, so I'm converting this to use
> ktime_get_real_ts64() as a safe replacement. I considered using
> ktime_get_real() instead, but since the algorithm here depends
> on the exact timing, I decided to introduce fewer changes
> and leave the code that determines the nanoseconds since the
> last seconds wrap untouched.
> 
> It's not entirely clear to me whether we should also change the
> time base to CLOCK_BOOTTIME or CLOCK_TAI. With boottime, we
> would be independent of changes due to settimeofday() and only
> see the speed adjustment from the upstream clock source, with
> the downside of having the signal be at an arbirary offset
> from the start of the UTC second signal. With CLOCK_TAI, we
> would use the same offset from the UTC second as before and
> still suffer from settimeofday() adjustments, but would be
> less confused during leap seconds.
> 
> Both boottime and tai only offer usable (i.e. avoiding ktime_t
> to timespec64 conversion) interfaces for ktime_t though, so
> either way, changing it wouldn't take significantly more work.
> CLOCK_MONOTONIC could be used with ktime_get_ts64(), but would
> lose synchronization across a suspend/resume cycle, which seems
> worse.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Rodolfo Giometti <giometti@...eenne.com>

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